Attempts are being made to develop adoptive immunotherapeutic techniques utilizing the transfer of cells grown in long-term culture in interleukin-2. Techniques for the prolonged growth of cytotoxic and proliferative T cell lines and clones with anti-tumor reactivity have been developed. These cells have been shown to mediate the immunologic rejection of allografts and syngeneic tumors and attempts to use these cells in the adoptive immunotherapy of mouse and human tumors are in progress. A new class of cytotoxic cells has been described in both the mouse and the human. These lymphokine activated killer (LAK) cells develop selective cytotoxicity for cancer cells following incubation in the lymphokine, interleukin-2. The adoptive transfer of these cells into mice bearing established tumors can mediate the inhibition of pulmonary metastases. The systemic administration of interleukin-2 has been shown to enhance immune responses in vivo. In the past year, two new immunotherapeutic trials have begun that utilize the adoptive transfer of lymphokine activated killer cells into patients with advanced cancer. In the past year, we have characterized a new recombinant interleukin-2 in the human and have begun clinical trials to study the in vivo effects of systemic administration of this material.